Matching Items (5)

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Optimal sampling for linear function approximation and high-order finite difference methods over complex regions

Description

I focus on algorithms that generate good sampling points for function approximation. In 1D, it is well known that polynomial interpolation using equispaced points is unstable. On the other hand,

I focus on algorithms that generate good sampling points for function approximation. In 1D, it is well known that polynomial interpolation using equispaced points is unstable. On the other hand, using Chebyshev nodes provides both stable and highly accurate points for polynomial interpolation. In higher dimensional complex regions, optimal sampling points are not known explicitly. This work presents robust algorithms that find good sampling points in complex regions for polynomial interpolation, least-squares, and radial basis function (RBF) methods. The quality of these nodes is measured using the Lebesgue constant. I will also consider optimal sampling for constrained optimization, used to solve PDEs, where boundary conditions must be imposed. Furthermore, I extend the scope of the problem to include finding near-optimal sampling points for high-order finite difference methods. These high-order finite difference methods can be implemented using either piecewise polynomials or RBFs.

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Agent

Created

Date Created
  • 2019

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Validation of a numerical model for design of geomembranes subject to extreme loads

Description

A numerical model for design of the geomembrane elements of waste containment systems has been validated by laboratory testing. Due to the absence of any instrumented case histories of seismic

A numerical model for design of the geomembrane elements of waste containment systems has been validated by laboratory testing. Due to the absence of any instrumented case histories of seismic performance of geomembrane liner systems, a large scale centrifuge test of a model geomembrane-lined landfill subject to seismic loading was conducted at the University of California at Davis Centrifuge Test facility as part of National Science Foundation Network for Earthquake the Engineering Simulation Research (NEESR) program. Data collected in the large scale centrifuge test included waste settlement, liner strains and earthquake accelerations at various locations throughout the model. This data on landfill and liner seismic performance has been supplemented with additional laboratory and small scale centrifuge tests to determine the parameters required for the numerical model, including strength and stiffness of the model materials, interface shear strengths, and interface stiffness. The numerical model explicitly assesses the forces and strains in the geomembrane elements of a containment system to subject to both static and seismic loads the computer code FLACTM, a finite difference program for non-linear analysis of continua. The model employs a beam element with zero moment of inertia and with interface elements on both sides to model to represent the geomembrane elements in the liner system. The model also includes non-linear constitutive models for the stress-strain behavior of geomembrane beam elements and an elastic-perfectly plastic model for the load-displacement behavior of the beam interfaces. Parametric studies are conducted with the validated numerical model to develop recommendations for landfill design, construction, and construction quality assurance.

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Agent

Created

Date Created
  • 2017

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Optical simulation and optimization of light extraction efficiency for organic light emitting diodes

Description

Current organic light emitting diodes (OLEDs) suffer from the low light extraction efficiency. In this thesis, novel OLED structures including photonic crystal, Fabry-Perot resonance cavity and hyperbolic metamaterials were numerically

Current organic light emitting diodes (OLEDs) suffer from the low light extraction efficiency. In this thesis, novel OLED structures including photonic crystal, Fabry-Perot resonance cavity and hyperbolic metamaterials were numerically simulated and theoretically investigated. Finite-difference time-domain (FDTD) method was employed to numerically simulate the light extraction efficiency of various 3D OLED structures. With photonic crystal structures, a maximum of 30% extraction efficiency is achieved. A higher external quantum efficiency of 35% is derived after applying Fabry-Perot resonance cavity into OLEDs. Furthermore, different factors such as material properties, layer thicknesses and dipole polarizations and locations have been studied. Moreover, an upper limit for the light extraction efficiency of 80% is reached theoretically with perfect reflector and single dipole polarization and location. To elucidate the physical mechanism, transfer matrix method is introduced to calculate the spectral-hemispherical reflectance of the multilayer OLED structures. In addition, an attempt of using hyperbolic metamaterial in OLED has been made and resulted in 27% external quantum efficiency, due to the similar mechanism of wave interference as Fabry-Perot structure. The simulation and optimization methods and findings would facilitate the design of next generation, high-efficiency OLED devices.

Contributors

Agent

Created

Date Created
  • 2016

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Effect of waste settlement and seismic loading on the integrity of geomembrane barrier systems

Description

The objective of the research is to develop guidelines for identifying when settlement or seismic loading presents a threat to the integrity of geosynthetic elements for both side slope and

The objective of the research is to develop guidelines for identifying when settlement or seismic loading presents a threat to the integrity of geosynthetic elements for both side slope and cover systems in landfills, and advance further investigation for parameters which influence the strains in the barrier systems. A numerical model of landfill with different side slope inclinations are developed by the two-dimensional explicit finite difference program FLAC 7.0, beam elements with a hyperbolic stress-strain relationship, zero moment of inertia, and interface elements on both sides were used to model the geosynthetic barrier systems. The resulting numerical model demonstrates the load-displacement behavior of geosynthetic interfaces, including whole liner systems and dynamic shear response. It is also through the different results in strains from the influences of slope angle and interface friction of geosynthetic liners to develop implications for engineering practice and recommendations for static and seismic design of waste containment systems.

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Agent

Created

Date Created
  • 2013

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Cooling strategy for effective automotive power trains: 3D thermal modeling and multi-faceted approach for integrating thermoelectric modules into proton exchange membrane fuel cell stack

Description

Current hybrid vehicle and/or Fuel Cell Vehicle (FCV) use both FC and an electric system. The sequence of the electric power train with the FC system is intended to achieve

Current hybrid vehicle and/or Fuel Cell Vehicle (FCV) use both FC and an electric system. The sequence of the electric power train with the FC system is intended to achieve both better fuel economies than the conventional vehicles and higher performance. Current hybrids use regenerative braking technology, which converts the vehicles kinetic energy into electric energy instead of wasting it. A hybrid vehicle is much more fuel efficient than conventional Internal Combustion (IC) engine and has less environmental impact The new hybrid vehicle technology with it's advanced with configurations (i.e. Mechanical intricacy, advanced driving modes etc) inflict an intrusion with the existing Thermal Management System (TMS) of the conventional vehicles. This leaves for the opportunity for now thermal management issues which needed to be addressed. Till date, there has not been complete literature on thermal management issued of FC vehicles. The primary focus of this dissertation is on providing better cooling strategy for the advanced power trains. One of the cooling strategies discussed here is the thermo-electric modules.

The 3D Thermal modeling of the FC stack utilizes a Finite Differencing heat approach method augmented with empirical boundary conditions is employed to develop 3D thermal model for the integration of thermoelectric modules with Proton Exchange Membrane fuel cell stack. Hardware-in-Loop was designed under pre-defined drive cycle to obtain fuel cell performance parameters along with anode and cathode gas flow-rates and surface temperatures. The FC model, combined experimental and finite differencing nodal net work simulation modeling approach which implemented heat generation across the stack to depict the chemical composition process. The structural and temporal temperature contours obtained from this model are in compliance with the actual recordings obtained from the infrared detector and thermocouples. The Thermography detectors were set-up through dual band thermography to neutralize the emissivity and to give several dynamic ranges to achieve accurate temperature measurements. The thermocouples network was installed to provide a reference signal.

The model is harmonized with thermo-electric modules with a modeling strategy, which enables optimize better temporal profile across the stack. This study presents the improvement of a 3D thermal model for proton exchange membrane fuel cell stack along with the interfaced thermo-electric module. The model provided a virtual environment using a model-based design approach to assist the design engineers to manipulate the design correction earlier in the process and eliminate the need for costly and time consuming prototypes.

Contributors

Agent

Created

Date Created
  • 2014